1. Field
Methods and apparatuses consistent with exemplary embodiments relate to an enhanced data processing apparatus employing a multiple-block based pipeline and an operation method thereof, and more particularly, to a method and an apparatus for decoding an image by accessing a memory device via a block group including a plurality of blocks to perform a parallel-pipeline decoding process on the block group.
2. Description of the Related Art
When images or sounds are transformed into digital data, a size of the transformed digital data is quite large. If the digital data is not compressed, the digital data occupies a significantly large space in memory and large bandwidth is necessary for transmission of such large-sized data. Therefore, a compression technique for reducing the size of digital data is necessary, and efficiency of storage space utilization and data transmission via a network may be improved by employing a compression technique.
Examples of image compression formats include GIF and JPEG. Examples of video and sound compression formats include MPEG, H.263, H.264/AVC, and H.265 (HEVC). High efficiency video coding (referred to hereinafter as ‘HEVC’) is the latest video coding standard and was introduced by the Joint Collaborative Team on Video Coding (JCT-VC) in 2013.
HEVC introduced a coding unit (CU) having a hierarchically recursive quadtree split structure, instead of a fixed-sized macro block employed in conventional image coding standards, such as H.264/AVC. Compared to conventional image coding standards, HEVC exhibits significantly improved compression efficiency due to the quadtree structure, but the calculation complexity is correspondingly significantly increased. One frame is split into maximum coding units (MCUs) having sizes, for example up to 64×64 or 128×128, and the maximum coding unit may be repeatedly split until the maximum coding unit is split into smallest coding units (SCUs) having sizes of 8×8 or 4×4, for example.
Furthermore, an input video stream is split into groups of pictures (GOP), which each include a series of pictures or frames. Each GOP includes a plurality of pictures, and each picture is split into a plurality of slices. Furthermore, two types of pictures may appear within a single GOP, that is, an intra mode picture (or I-picture) and a prediction motion-compensated picture (P-picture or B-picture).
In an I-picture, all blocks are decoded in an intra mode without motion compensation. Only a unidirectional prediction for selecting a reference picture from a single reference picture list may be performed with regard to a P-picture, whereas a bidirectional prediction employing two reference picture lists and a unidirectional prediction employing a single reference picture list may be selectively employed with regard to a B-picture. The prediction motion-compensated picture (P-picture or B-picture) may be decoded in an inter mode, in which each block utilizes motion compensation.
An image decoding system generally includes a memory for storing an input video stream and frames for performing motion compensation.
In the image decoding system, memory accesses may include: 1) a memory access for entropy-decoding, 2) a memory access for inter mode prediction with regard to each block size, 3) a memory access with respect to surrounding blocks for intra mode prediction, 4) a memory access for filtering, and 5) a memory access for writing a final reconstructed image to a memory. The access with respect to surrounding blocks for intra mode prediction and memory access for filtering may use internal memory. Particularly, from among the memory accesses, the memory access for inter mode prediction requires the largest memory bandwidth.
H.265/HEVC, which has been recently suggested as a new international moving picture coding standard, employs various blocking processing units and significantly more complicated techniques for motion prediction and motion compensation, as compared to conventional image coding standards. Thus, frequency of memory access for motion compensation is significantly increased. Therefore, there is a demand for an efficient memory accessing technique for an image decoding apparatus. Furthermore, because H.264/AVC employs a 16×16 macro block (MB) as the only basic processing unit, there is a demand for an efficient memory accessing technique due to a large quantity of memory accesses for motion compensation in the instance of processing a large image, e.g., an ultra high definition (UHD) image.